The jacket determines the rate of bullet expansion in a game animal or the target. There are different types of jackets for varmints, deer, large animals and paper targets. In some cases, you want quick expansion and in other cases you want controlled expansion and deep penetration. For targets, you want a bullet that has the desired shape for the distance being shot and as near perfect concentricity and weight distribution as you can get.

Full metal jacket bullets (FMJ) are typically used by the military because of the Geneva Convention requirements that “dum-dum” or expanding/fragmenting bullets not be used on personnel. FMJ bullets are used on some game animals to ensure deep penetration and/or minimal pelt damage.

The shape of a high performance bullet is often controlled by the jacket. Spire points, hollow points, boat tails, dual cores, ballistic tips and other features are facilitated by jacket engineering.

Target bullets have very uniform jackets and may have hollow points to remove weight from the nose of the bullet. Target hollow points will make a hole in a game animal but may not expand like a hunting hollow point.

Very often, a jacket is tailored to a specific cartridge like a 30/30 Winchester to provide reliable expansion at lower velocities. Such a bullet shot out of a .30 magnum at a high velocity and rotation may come apart in flight or disintegrate upon impact without much penetration.

It often pays to ask questions of knowledgeable persons when selecting a specific bullet and cartridge.

PerazziBigBore- I agree that graphite does help shot flow during the reloading process but I have some difficulty visualizing how it helps shot "flow" when it is traveling through the barrel. There is some set back of the shot in the shot cup but in a restricted space, how could graphite reduce this?